Synthesis, isolation, and isomerization of two stereoisomers of 2,3,7,8-tetramethyl-5,10-di(p-tolyl)-5,10-dihydrostibanthrene

✍ Scribed by Yosuke Uchiyama

• Publisher: John Wiley and Sons
• Year: 2011
• Tongue: English
• Weight: 295 KB
• Volume: 22
• Category: Article
• ISSN: 1042-7163
• DOI: 10.1002/hc.20693

✦ Synopsis

Abstract

Two stereoisomers, trans form 1a and cis form 1b, of 2,3,7,8‐tetramethyl‐5,10‐di(p‐tolyl)‐5,10‐dihydrostibanthrene (1) were successfully synthesized. Both of 1a and 1b were characterized by X‐ray crystallographic analysis, which revealed the orientations of two p‐tolyl groups at the 5,10‐positions, the configurations at the antimony and the conformation of the central tricyclic system. DFT calculations [B3LYP/6‐31G(d) for C and H, LANL2DZ for Sb] of 5,10‐diphenyl‐5,10‐dihydrostibanthrene (3) were performed to give three optimized structures trans 3a, cis_exo 3b′, and cis_endo 3b′′, in the ground states, 3a being the most stable. The trans–cis isomerization of 1 was observed in 1‐chloronaphthalene at above ca. 200°C and was revealed to occur via vertex inversion at the antimony, because the energy barrier of the configurational isomerization was estimated to have high inversion barrier by kinetics and the isomerization showed no solvent effect. On the other hand, the trans–trans and the cis_exo–cis_endo isomerization of 1 were not observed even at −102°C in a CD~2~Cl~2~ solution, indicating that the conformational isomerization has quite low energy barriers and proceeds via skeletal inversion of the tricyclic system. The energy barrier of the conformational isomerization was estimated to be much lower than that of the configurational exchange by DFT calculations of searching for transition state using the synchronous transit‐guided quasi‐Newton (STQN) method. © 2011 Wiley Periodicals, Inc. Heteroatom Chem 22:377–387, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/hc.20693